ESD is the sudden release of electricity from one charged object to another when the two objects come into contact or close proximity. ESD diodes are electrostatic suppressor diodes designed to protect integrated circuits (IC). ESD diodes are used to protect various data interfaces such as ethernet, USB, and so on, and are connected in reverse direction. Under normal operation with forward voltage applied, they are inactive and conduct zero current. As the ESD diode experiences reverse voltage it consumes some minimal (leakage) current. In the event of an ESD strike where the voltage exceeds its rated reverse breakdown voltage, the ESD diode creates a low impedance path diverting current flow to ground. The ESD diode limits the peak voltage and current, thereby protecting the downstream IC. For additional description of ESD events, system design considerations, and parameter terminology please refer to TI's System-Level ESD Protection Guide.

Typically, a diode is referred to as ESD type if it includes protections for system-level IEC61000-4-2 testing methods such as contact discharge or air-gap discharge. In the contact-discharge method, the test-simulator electrode is held in contact with the device under test (DUT). In air-gap discharge, the charged electrode of the simulator approaches the DUT, and a spark to the DUT actuates the discharge. For more information on IEC test procedures please refer to Design considerations for system-level ESD circuit protection.

These are not to be confused with device-level testing methods like human body model (HBM), charge device model (CDM), and machine model (MM). Device-level HBM, CDM, and MM tests are intended to verify only that integrated circuits survive the manufacturing process, while system-level tests specified by IEC 61000-4-2 are intended to simulate end-user ESD events in the real world.

In high-speed data transmission applications, ESD diodes have low capacitance to maintain signal integrity and minimize signal distortion. The target ESD capacitance varies by interface type (USB, Ethernet, CAN FD / XL, etc.). More information can be found in the following engineer to engineer (e2e) forum post on recommended max capacitance for various interfaces: (2) [FAQ] What TI ESD/TVS diode should I use to protect Interfaces in my system? - Interface forum - Interface - TI E2E support forums